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PubMed2003

Evidence of a preferred molecular pathway in patients with synchronous colorectal cancer.

BACKGROUND: A small proportion of patients with colorectal carcinoma (CRC) have synchronous tumors at the time of diagnosis. A subset of sporadic CRCs display microsatellite instability (MSI) that is associated with MLH1 silencing due to promoter methylation. In the current study, the authors investigated the proportion of tumors with MSI in patients with synchronous colorectal carcinoma (SCRC) and the concordance in MSI status among tumors in a given individual. In addition, the authors examined MLH1 and MSH2 expression and MLH1 promoter methylation in SCRCs. METHODS: The current study included 77 patients, with a combined total of 170 invasive SCRCs, who were identified from a database of 2884 patients with CRC. Instability was determined by polymerase chain reaction (PCR) amplification using a set of five markers. Tumors that were unstable at two or more markers were considered unstable (MSI); otherwise, they were considered microsatellite stable (MSS). Expression of MLH1 and MSH2 was determined by immunohistochemistry. Methylation of the MLH1 gene promoter was determined by a methylation-specific PCR assay. Statistical comparisons were made using the chi-square test or the Student t test. RESULTS: Of the 77 patients in the study, 21 (27%) had a family history of hereditary nonpolyposis colon carcinoma-related malignancy, but none fulfilled the Amsterdam II criteria. Fifty-four of 170 tumors (32%) were found to be MSI. Patients with MSI tumors were older and more frequently female. All but 1 MSI tumor lacked expression of MLH1 (n = 44) or MSH2 (n = 8), or both (n = 1). All MLH1-negative tumors, compared with only 3 MLH1-positive tumors, were methylated at the MLH1 promoter. Most patients (n = 67; 87%) had either all MSS tumors (n = 48; 62%) or all MSI tumors (n = 19; 25%); 10 patients (13%) had both MSS and MSI tumors. The observed MSI/MSS distribution was significantly different from the distribution expected based on an assumption of independence (P < 0.0001). CONCLUSIONS: There is a strong concordance in MSI/MSS status among tumors in the same individual. This finding suggests that the tumors in patients with SCRC develop along a preferred molecular pathway.

Adaptor Proteins, Signal Transducing↗
PubMed2006

Tumor buds show reduced expression of laminin-5 gamma 2 chain in DNA mismatch repair deficient colorectal cancer.

PURPOSE: Tumor budding at the invasive margin of colorectal cancer is an important adverse prognostic factor. The subset of colorectal cancer that is deficient in DNA mismatch repair has been associated with a good prognosis. It is hypothesized that tumor budding in this subset may lack biologic aggressiveness because it is not associated with aberrant expression of the independent prognostic factor, laminin-5 gamma 2. METHODS: Eighty colorectal cancers with high-grade tumor budding were studied, including nine sporadic colorectal cancers with immunohistochemical loss of expression of MLH1 (MLH1(-)), seven colorectal cancers from patients with hereditary nonpolyposis colorectal cancer, and 64 sporadic colorectal cancers expressing both MLH1 and MSH2 (MLH1(+)). Two regulatory mechanisms for laminin-5 gamma 2 expression were explored, including aberrant nuclear expression of beta-catenin by immunohistochemistry and promoter methylation of laminin-5 gamma 2 by methylation-specific polymerase chain reaction. RESULTS: Only three of nine MLH1(-) colorectal cancers showed expression of laminin-5 gamma 2 compared with 46 of 64 MLH1(+) colorectal cancers (P = 0.05). Only two of seven hereditary nonpolyposis colorectal cancers expressed laminin-5 gamma 2 compared with MLH1(+) colorectal cancers (P= 0.03). Expression of nuclear beta-catenin was more frequent (58 percent) in MLH1(+) colorectal cancers compared with MLH1(-) colorectal cancers (11 percent, P = 0.01). Methylation of laminin-5 gamma 2 was found in 5 of 38 (13 percent) cases but did not differ among colorectal cancer subsets. Four of five colorectal cancers with methylation of laminin-5 gamma 2 were scored as negative for laminin-5 gamma 2 by immunohistochemistry. CONCLUSIONS: The reduced expression of laminin-5 gamma 2 in colorectal cancers with deficient DNA mismatch repair may underlie a variant of tumor budding that is relatively nonaggressive.

Adaptor Proteins, Signal Transducing↗
PubMed2004

Mismatch repair gene expression and genetic instability in testicular germ cell tumor.

Human mismatch repair (MMR) genes encode highly conserved interacting proteins that correct replication errors predisposing to hereditary gastrointestinal and genitourinary malignancies. A subset of sporadic genitourinary tumors also exhibits MMR deficiency and can be identified by measuring the frequency of microsatellite instability (MSI) in cancer cell DNA. We investigated expression of the two most commonly mutated MMR genes, MSH2 and MLH1, in sporadic testicular germ cell tumor (GCT) in order to: (1) determine the expression pattern of MSH2 and MLH1 proteins in normal seminiferous tubules and histologically distinct GCT subtypes, (2) correlate MMR gene expression with genetic instability in GCT and (3) develop a panel of molecular markers that can identify genetically distinct subsets of GCT for prognostic assessment. MSH2 and MLH1 had differential staining patterns in normal seminiferous tubules and malignant tissues. MSH2 was expressed in all stages of spermatogenesis up to but excluding mature sperm whereas MLH1 was predominantly expressed in premeiotic germ cells. All histological GCT subtypes showed differential immunostaining for MSH2 and MLH1 however pure seminoma had statistically significant fewer low MSH2 staining tumors than other subtypes (p = 0.046). Twenty-five percent of GCT exhibited increased frequency of MSI (MSI+ tumors) with 73, 70 and 43% of MSI+ tumors exhibiting low MSH2, low MLH1 or low MSH2 and low MLH1 staining respectively. Fifteen percent of testicular GCT exhibited loss of heterozygosity (LOH) but no MSI (LOH only tumors). Only 28, 17 or 6% of LOH only tumors exhibited low MSH2, low MLH1 or low MSH2 and low MLH1 staining respectively.

Adaptor Proteins, Signal Transducing↗
PubMed1998

Colorectal and extracolonic cancer variations in MLH1/MSH2 hereditary nonpolyposis colorectal cancer kindreds and the general population.

PURPOSE: This clinical case review aimed to identify phenotypic variations in colorectal and extracolonic cancer expression between hereditary nonpolyposis colorectal cancer (HNPCC) families with MLH1 and MSH2 germline mutations and the general population. METHODS: Colorectal cancer onset and site distribution were compared among 67 members of MLH1 kindreds, 45 members of MSH2 kindreds, and 1,189 patients from the general population. Synchronous and metachronous cancer rates, tumor stage, extracolonic cancer incidence, and survival were also compared. RESULTS: Mean ages of colorectal cancer onset were 44, 46, and 69 years for MLH1, MSH2, and the general population, respectively (P < 0.001). More proximal and fewer distal colon cancers were noted in HNPCC than the general population (P < 0.001, P = 0.04). Site distribution showed disparity of rectal cancers (8 percent MLH1 vs. 28 percent MSH2; P = 0.01) based on genotypes. Overall, synchronous colorectal cancer rates were 7.4, 6.7, and 2.4 percent for MLH1, MSH2, and the general population, respectively (P = 0.016). Annual metachronous colorectal cancer rates were 2.1, 1.7, and 0.33 percent for MLH1, MSH2, and the general population, respectively (P = 0.041). Colorectal cancer stage presentation was lower in HNPCC than the general population (P = 0.0028). Extracolonic cancers were noted in 33 percent of MSH2 patients, compared with 12 percent of MLH1 patients and 7.3 percent of the general population with colorectal cancers (P < 0.001). Combined MLH1 and MSH2 ten-year survival was 68.7 percent compared with 47.8 percent for the general population (P = 0.009 stage stratified, hazard ratio 0.57). CONCLUSION: The presence of rectal cancer should not preclude the diagnosis of HNPCC, because the incidence of rectal cancer in MSH2 was comparable with that in the general population. Phenotypic variations, including the preponderance of extracolonic cancers in MSH2 patients, did not result in survival differences between genotypic subgroups. These phenotypic features of HNPCC genotypes may have clinical significance in the design of specific screening, surveillance, and follow-up for affected individuals.

Adaptor Proteins, Signal Transducing↗
PubMed2006

Enhanced detection of microsatellite instability and mismatch repair gene expression in cutaneous squamous cell carcinomas.

BACKGROUND: Microsatellite instability (MSI) is a phenotypic characteristic of tumors with biallelic inactivation of mismatch repair genes, such as MSH2 or MLH1, and contributes to malignant transformation. AIMS: The aim of this study was to examine the prevalence of MSI in cutaneous squamous cell carcinoma (SCC) using a PCR and fluorescent-based detection system. These methods of analysis offer several advantages over the use of silver staining and autoradiographic techniques. We also aimed to determine if MSI status correlated with expression of the MSH2 and MLH1 mismatch repair proteins in these cutaneous SCC samples. METHODS: The MSI status of 22 histologically confirmed invasive cutaneous SCC samples were analyzed at five microsatellite markers (the National Cancer Institute's Bethesda panel of two mononucleotide and three dinucleotide markers) using a PCR and fluorescent-based detection system. Immunohistochemical analysis of MSH2 and MLH1 protein expression was also carried out on the SCC samples. RESULTS: Only one case of cutaneous SCC displayed MSI. This was found at just one of five markers, and thus was low frequency MSI. All 22 cutaneous SCC cases strongly expressed MSH2 protein. Eighteen (82%) of the cutaneous SCC cases showed moderate to strong expression of MLH1 protein. The remaining four cases of cutaneous SCC were negative for MLH1 protein. Therefore, the majority of the SCC patients analyzed showed a correlation between absence of MSI and expression of MSH2 and MLH1 proteins. CONCLUSIONS: MSI is uncommon in cutaneous SCC. In addition, MSH2 was strongly expressed in all SCC samples analyzed and appeared to be upregulated when compared with the corresponding normal tissue. MLH1 protein was not detected in 4 of 22 SCC cases, although it was expressed in the corresponding normal tissue, suggesting that inactivation of MLH1 may be a late event in a subset of invasive SCC cases.

Adaptor Proteins, Signal Transducing↗
PubMed2002

Immunohistochemical pattern of MLH1/MSH2 expression is related to clinical and pathological features in colorectal adenocarcinomas with microsatellite instability.

Detection of colorectal carcinomas with high-frequency microsatellite instability (MSI-H) is clinically important for several reasons. Recent studies suggested that immunohistochemical analysis of MLH1 and MSH2 expression is a rapid and accurate method for identifying large bowel tumors of the MSI-H phenotype. In this study, we evaluated by immunohistochemistry MLH1 and MSH2 protein expression in 132 MSI-H, 23 MSI-L (low-frequency MSI), and 150 microsatellite stable (MSS) colorectal adenocarcinomas. Loss of MLH1 or MSH2 expression was detected in 120 (90.9%) MSI-H carcinomas, whereas all MSI-L and MSS tumors showed normal expression of both proteins. Lack of MLH1 nuclear staining was observed much more often than absence of MSH2 nuclear staining (106 and 14 cases, respectively). Among MSI-H carcinomas, MLH1/MSH2 pattern of expression was significantly related to several clinical and pathological variables. In particular, MSI-H MLH1/MSH2-positive carcinomas were more often located in the distal colon, were more frequently classified as ordinary adenocarcinomas, and were more likely to be well or moderately differentiated, p53 positive, and <7 cm in diameter than were MLH1-negative and MSH2-negative carcinomas. In addition, MLH1-negative carcinomas were less common among patients with hereditary nonpolyposis colorectal cancer (HNPCC) or suspected HNPCC and in the group of patients aged <50 years. Patients with MLH1-negative carcinomas more frequently died of disease than did patients with MLH1/MSH2-positive and MSH2-negative MSI-H tumors, but the difference was not statistically significant. The results of the present investigation strongly indicate that immunohistochemical analysis of MLH1 and MSH2 expression is a practical and reliable method for the routine detection of the vast majority of MSI-H large bowel adenocarcinomas. Our data also point out that MSI-H MLH1/MSH2-positive colorectal carcinomas are characterized by distinctive pathological features.

Adaptor Proteins, Signal Transducing↗
PubMed2004

Lynch Syndrome

CLINICAL CHARACTERISTICS: Lynch syndrome is characterized by an increased risk for colorectal cancer (CRC) and cancers of the endometrium, ovary, stomach, small bowel, urinary tract, biliary tract, prostate, brain (usually glioblastoma), skin (sebaceous adenomas, sebaceous epithelioma, sebaceous carcinomas, and keratoacanthomas), and pancreas. Cancer risks and age of onset vary depending on the associated gene. Several other cancer types have been reported to occur in individuals with Lynch syndrome (e.g., sarcomas, adrenocortical carcinoma). However, the data are not sufficient to demonstrate that the risk of developing these cancers is increased in individuals with Lynch syndrome. DIAGNOSIS/TESTING: The diagnosis of Lynch syndrome is established in a proband with a germline heterozygous pathogenic variant in MLH1, MSH2, MSH6, or PMS2 or a 3' EPCAM deletion identified by molecular genetic testing, or, rarely, constitutional inactivation of the MLH1 promotor due to methylation identified by DNA methylation analysis. MANAGEMENT: Treatment of manifestations: Polypectomy at the time of colonoscopy; referral to advanced endoscopist for lesions requiring advanced resection techniques; surgical resection of polyps when needed; individualized surgical management for colon cancer based on tumor location, stage, Lynch syndrome-associated gene, age, comorbidity, bowel function, anticipated quality of life, and risk of metachronous CRC; mismatch repair (MMR) testing, microsatellite instability (MSI) testing, and multidisciplinary evaluation for rectal cancer prior to treatment; consider immune checkpoint inhibitor therapy for metastatic or unresectable MMR-deficient or MSI-high tumors; other tumors are managed as in the general population. Prevention of primary manifestations: Risk-reducing hysterectomy with bilateral salpingo-oophorectomy can be considered after childbearing is completed. Prophylactic colectomy prior to the development of colon cancer is generally not recommended for individuals known to have Lynch syndrome because screening colonoscopy with polypectomy is an effective preventive measure. Aspirin therapy has been shown to decrease the risk for CRC in individuals with Lynch syndrome. Surveillance: Colonoscopy with removal of precancerous polyps with frequency and initial screening based on gene involved and family history; annual education for females regarding the symptoms of endometrial and ovarian cancers; consider transvaginal ultrasound examination and endometrial biopsy every one to two years beginning at age 30 to 35 years; consider upper endoscopy examination particularly for individuals with a family history of gastric cancer and those of Asian ancestry with frequency and initial screening based on gene involved and family history; biopsies should be evaluated for H pylori infections so that appropriate treatment can be given as needed; consider capsule endoscopy and small bowel enterography for distal small bowel cancers in symptomatic persons; consider urinalysis with urine cytology annually beginning between ages 30 and 35 years; consider pancreatic cancer screening in individuals with a family history of pancreatic cancer; follow population screening guidelines and maintain awareness for signs and symptoms of other cancers. Agents/circumstances to avoid: Obesity, physical inactivity, cigarette smoking, alcohol consumption, and type 2 diabetes may increase CRC risk in individuals with Lynch syndrome. Evaluation of relatives at risk: Molecular genetic testing for the familial Lynch syndrome-related pathogenic variant is recommended for all first-degree relatives (parents, sibs, and offspring) of an affected individual in order to identify as early as possible those who would benefit from surveillance, risk-reducing interventions, and other preventive measures. Testing for constitutional MLH1 hypermethylation is recommended for all first-degree relatives of individuals with Lynch syndrome caused by constitutional MLH1 methylation. GENETIC COUNSELING: Lynch syndrome caused by a heterozygous germline Lynch syndrome-related pathogenic variant (i.e., a pathogenic variant in MLH1, MSH2, MSH6, or PMS2 or a 3' EPCAM deletion) is inherited in an autosomal dominant manner. Individuals with Lynch syndrome caused by constitutional inactivation of MLH1 by methylation typically represent simplex cases, although affected individuals from a few families have been reported with inherited MLH1 promoter methylation. The majority of individuals with a heterozygous germline Lynch syndrome-related pathogenic variant inherited the pathogenic variant from a parent who may or may not have had cancer. Each child of an individual with Lynch syndrome has a 50% chance of inheriting the Lynch syndrome-related pathogenic variant and the related cancer risks. If the reproductive partner of an individual with Lynch syndrome has a germline heterozygous pathogenic variant in the same Lynch syndrome-related gene, offspring are at risk of inheriting biallelic pathogenic variants and having constitutional mismatch repair deficiency. Once a germline Lynch syndrome-related pathogenic variant has been identified in an affected family member, predictive testing for at-risk asymptomatic family members and prenatal/preimplantation genetic testing are possible.

Hereditary Non-Polyposis Colorectal Cancer (HNPCC)↗
PubMed2004

Association of colonic and endometrial carcinomas in Portuguese families with hereditary nonpolyposis colorectal carcinoma significantly increases the probability of detecting a pathogenic mutation in mismatch repair genes, primarily the MSH2 gene.

BACKGROUND: Hereditary nonpolyposis colorectal carcinoma (HNPCC) significantly raises the risk of developing colorectal carcinoma (CRC) and other extracolonic tumors. It is defined by the Amsterdam Criteria and is associated with germline mutations in mismatch repair genes, primarily MLH1 and MSH2. The objectives of the current study were to evaluate the presence of CRC (Type I) and other extracolonic tumors (Type II) in families with HNPCC and to analyze the findings for correlations with germline mutations in the MLH1 and MSH2 genes. METHODS: Seventy families with an HNPCC diagnosis were analyzed. Denaturing gradient gel electrophoresis and direct sequencing were used for germline mutation analysis in the MLH1 and MSH2 genes. RESULTS: Forty-three of 70 families (61%) presented with HNPCC Type II. In 21 of 30 families that had a complete genetic diagnosis, 16 pathogenic germline mutations (7 MLH1 mutations and 9 MSH2 mutations) and 5 mutations of unknown pathogenecity (all MLH1 mutations) were found. In the remaining nine families, no mutations were detected. Unequivocally pathogenic mutations were far more common in families with HNPCC Type II compared with families that had CRC only (P = 0.01). Families with endometrial carcinoma presented with the greatest probability of mutational detection (P = 0.005). MLH1 was only gene affected in families with HNPCC Type I, whereas mutations in both MLH1 and MSH2 were found in families with HNPCC Type II (P = 0.04). However, the MSH2 gene was more frequently involved in families with HNPCC in which endometrial carcinoma was present (P = 0.005). CONCLUSIONS: CRC and endometrial carcinoma were associated with a greater probability of detecting pathogenic mutations in mismatch repair genes, with MSH2 involvement predominating. The results support specific mutational screening strategies, based on observed phenotypes, for families with HNPCC.

Adaptor Proteins, Signal Transducing↗
PubMed2002

Multiple mutations are common at mouse Aprt in genotoxin-exposed mismatch repair deficient cells.

Mismatch repair deficiency is known to contribute to elevated rates of mutations, particularly at mono- and dinucleotide repeat sequences. However, such repeats are often missing from the coding regions of endogenous genes. To determine the types of mutations that can occur within an endogenous gene lacking highly susceptible repeat sequences, we examined mutagenic events at the 2.3 kb mouse Aprt gene in kidney cell lines derived from mice deficient for the PMS2 and MLH1 mismatch repair proteins. The Aprt mutation rate was increased 33-fold and 3.6-20-fold for Mlh1 and Pms2 null cell lines, respectively, when compared with a wild-type kidney cell line. For the Pms2 null cells this increase resulted from both intragenic events, which were predominantly base-pairs substitutions, and loss of heterozygosity events. Almost all mutations in the Mlh1 null cells were due to base-pair substitutions. A:T-->G:C transitions (54% of small events) were predominant in the Pms2 null cells whereas G:C-->A:T transitions (36%) were the most common base-pair change in the Mlh1 null cells. Interestingly, 4-9% of the spontaneous mutant alleles in the mismatch repair deficient cells exhibited two well-separated base-pair substitution events. The percentage of mutant alleles with two and occasionally three base-pair substitutions increased when the Pms2 and Mlh1 null cells were treated with ultraviolet radiation (15-21%) and when the Mlh1 null cells were treated with hydrogen peroxide (35%). In most cases the distance separating the multiple base-pair substitutions on a given allele was in excess of 100 base-pairs, suggesting that the two mutational events were not linked directly to a single DNA lesion. The significance of these results is discussed with regards to the roles for the PMS2 and MLH1 proteins in preventing spontaneous and genotoxin-related mutations.

Adaptor Proteins, Signal Transducing↗
PubMed2005

Association of mismatch repair deficiency with PTEN frameshift mutations in endometrial cancers and the precursors in a Japanese population.

We studied mismatch repair deficiency and PTEN (phosphatase and tensin homologue deleted on chromosome 10) mutations in endometrial cancers and hyperplasias in a Japanese population. Methylation-sensitive restriction enzyme polymerase chain reaction revealed MLH1 hypermethylation in 21 (38%) of 56 endometrial cancers. Sequencing analysis revealed PTEN mutations in 22 patients with cancer (39%) in exons 5 and 8. A PTEN frameshift mutation was associated significantly with MLH1 hypermethylation (P = .01) and a highly positive phenotype with microsatellite instability (P < .001) but not with a PTEN missense mutation. In hyperplasia, MLH1 hypermethylation was similarly observed (11/27 [41%]), but the PTEN mutation was less frequent (5/27 [19%]), observed only in atypical hyperplasias; among the 5 patients with a PTEN mutation, the 2 patients with frameshift mutations had MLH1 hypermethylation, but the 3 patients with missense mutations had unmethylated MLH1. These findings indicate that MLH1 hypermethylation is an early event frequently occurring in hyperplasia without atypia, whereas the PTEN mutation occurs later, mostly in atypical hyperplasia, possibly caused by MLH1 hypermethylation.

Adaptor Proteins, Signal Transducing↗
PubMed2000

A polymorphism in the ATM gene modulates the penetrance of hereditary non-polyposis colorectal cancer.

Germ-line mutations in MLH1 and MSH2 genes predispose to hereditary non-polyposis colorectal cancer (HNPCC) syndrome, but they do not predict a specific phenotype of the disease. We speculated that the ataxia-telangiectasia mutated gene (ATM) was a candidate gene to modulate the phenotypic expression of HNPCC, as heterozygous individuals for germ-line ATM mutations have been considered at higher risk of developing epithelial malignancies. The frequency of the ATM D1853N polymorphism was evaluated in 167 individuals from 20 HNPCC families in which MLH1 or MSH2 germ-line mutations co-segregated with the disease. Among the 67 MLH1 or MSH2 mutation carriers, the ATM 1853N variant was associated with a significantly higher incidence of colorectal and other HNPCC-related cancers, when compared with individuals carrying the ATM 1853D variant [12/13 (92%) vs. 31/54 (57.5%); p = 0.02]. MLH1 and MSH2 mutation carriers who concomitantly carried the ATM 1853N variant, had an 8 times increased risk of developing colorectal and other HNPCC-related cancers (OR: 8.9; p = 0.02), when compared with MLH1 or MSH2 mutation carriers with the ATM 1853D variant. Our results suggest that the ATM D1853N polymorphism modulates the penetrance of MLH1 and MSH2 germ-line mutations.

Adaptor Proteins, Signal Transducing↗
PubMed2001

Resistance to topoisomerase poisons due to loss of DNA mismatch repair.

Sporadic breast carcinomas demonstrate microsatellite instability, reflecting the presence of DNA mismatch repair-deficient cells, in about one fourth of cases at the time of diagnosis. Loss of DNA mismatch repair has been reported to result in resistance not only to cisplatin and alkylating agents but also to the topoisomerase II poison doxorubicin, suggesting an association between DNA mismatch repair and topoisomerase II poison-induced cytotoxicity. Our study investigates the relationship between loss of MSH2 or MLH1 function and sensitivity to the topoisomerase I and II poisons, and to the taxanes, 2 classes of cytotoxic drugs commonly used in breast cancer. Two pairs of cell lines proficient and deficient in mismatch repair due to loss of either MSH2 or MLH1 function were used. Loss of either MSH2 or MLH1 function resulted in resistance to the topoisomerase II poisons doxorubicin, epirubicin and mitoxantrone, whereas only loss of MLH1 function was associated with low-level resistance to the topoisomerase I poisons camptothecin and topotecan. In contrast, there was no resistance to docetaxel and paclitaxel. Our data support the hypothesis that both MSH2 and MLH1 are involved in topoisomerase II poison-mediated cytotoxicity, whereas only MLH1 is involved in topoisomerase I poison-mediated cytotoxicity. Since our study shows that loss of DNA mismatch repair does not result in resistance to the taxanes, these drugs can be recommended for use in breast cancer deficient in mismatch repair.

Adaptor Proteins, Signal Transducing↗
PubMed2005

Mechanisms of microsatellite instability in colorectal cancer patients in different age groups.

PURPOSE: The proportion of colorectal cancers located proximal to the splenic flexure increases with age. Colorectal cancers of the microsatellite instability phenotype are preferentially located in the proximal colon. We investigated the location of colorectal cancer with this phenotype in different age groups to determine whether different molecular mechanisms could account for the changes in distribution of colorectal cancers. METHODS: A representative sample of 230 colorectal cancers from three age groups (<45 years, 60-70 years, >87 years) was selected from a subset of The Upper Midwest Oncology Medical Registries database. Microsatellite instability was determined by polymerase chain reaction using a panel of five microsatellite markers. The presence of new microsatellite alleles at two or more loci was scored as microsatellite instability. Tumors were otherwise considered microsatellite stable. MLH1 and MSH2 expression was determined by immunohistochemistry. Methylation of the MLH1 gene promotor was determined by methylation-specific polymerase chain reaction assay. RESULTS: The proportion of tumors of the microsatellite instability phenotype was 21 percent in the young group, 15 percent in the middle group, and 33 percent in the old group. More tumors of the microsatellite instability phenotype were proximal compared with microsatellite-stable tumors in all three age groups, but the differences were significant only for the old group. Tumors of the microsatellite instability phenotype in the older group were associated with MLH1 inactivation (24/29 or 83 percent), MLH1 promoter methylation (18/29 or 62 percent), and proximal location (25/29 or 86 percent), while tumors in the young group were associated with MSH2 inactivation (8/18 or 44 percent) and distal location (11/18 or 62 percent). CONCLUSION: The age-related proximal shift of colorectal cancers is associated with the microsatellite instability phenotype, MLH1 inactivation, and MLH1 promoter hypermethylation.

Adaptor Proteins, Signal Transducing↗
PubMed2006

The added value of PMS2 immunostaining in the diagnosis of hereditary nonpolyposis colorectal cancer.

Identification and characterization of the genetic background in patients with the hereditary nonpolyposis colorectal cancer (HNPCC) syndrome is important since control programmes can in a cost-effective manner prevent cancer development in high-risk individuals. HNPCC is caused by germline mismatch repair (MMR) gene mutations and the genetic analysis of HNPCC therefore includes assessment of microsatellite instability (MSI) and immunohistochemical MMR protein expression in the tumor tissue. MSI is found in >95% of the HNPCC-associated tumors and immunostaining using antibodies against the MMR proteins MLH1, MSH2, and MSH6 has been found to correctly pinpoint the affected gene in about 90% of the cases. The PMS2 antibody was the most recently developed and we have in a clinical material assessed the added value of PMS2 immunostaining in 213 patients with suspected hereditary colorectal cancer. All 119 MSS tumors showed retained expression for all four antibodies and PMS2 did thus not identify any underlying MMR defect in these cases. However, PMS2 immunostaining contributed to the characterization of the MMR defect in a subset of the MSI tumors. Concomitant loss of MLH1 and PMS2, which functionally interact in the MutLalpha complex, was found in 98% of the tumors from patients with germline MLH1 mutations. Among the 12 MSI-high tumors with retained expression of MLH1, MSH2 and MSH6, 8 tumors showed loss of PMS2 staining, and mutations in MLH1 were identified in 2 and mutations in PMS2 in 3 of these individuals. In summary, isolated loss of PMS2 was found in 8% of the MSI-high tumors in our series, including 8/12 previously unexplained MSI-high tumors, in which mutations either in MLH1 or in PMS2 were identified in five cases.

Adaptor Proteins, Signal Transducing↗
PubMed2005

The mechanism of microsatellite instability is different in synchronous and metachronous colorectal cancer.

MLH1 promoter hypermethylation has been described as the primary mechanism for high-frequency microsatellite instability (MSI-H) in sporadic colorectal cancers (CRCs). The underlying molecular mechanism for microsatellite instability (MSI) in synchronous and metachronous CRCs is not well described. A total of 33 metachronous CRC patients and 77 synchronous CRC patients were identified from 2884 consecutive patients undergoing cancer surgery in an academic center. Evaluable tumors were tested for MSI, immunohistochemistry for MLH1 and MSH2 protein expression, and hypermethylation of the MLH1 promoter. MSI-H tumors were found in 12 (36%) metachronous CRC patients and 29 (38%) synchronous CRC patients. MSI-H metachronous CRC patients were younger at index cancer diagnosis (64 vs. 76 years, P=0.01) and more often were diagnosed before 50 years of age (4 of 12 vs. 0 of 29, P=0.005). Loss of MLH1 expression associated with promoter hypermethylation was common in all patients, although more common in MSI-H synchronous patients (50% metachronous vs. 83% synchronous, P=0.03). Overall, MLH1 promoter hypermethylation was seen in 7 of 17 (41%) metachronous and 44 of 54 (81%) synchronous MSI-H CRCs tested (P=0.004). Although MSI occurred with equal frequency among patients with synchronous and metachronous CRCs, the underlying mechanism for MSI was different. Observed differences in MLH1 promoter hypermethylation and patient characteristics suggest most MSI-H synchronous CRCs in our population were sporadic in origin. In contrast, more MSI-H metachronous CRCs were associated with patient and tumor characteristics suggestive of underlying hereditary nonpolyposis CRC.

Adaptor Proteins, Signal Transducing↗
PubMed2003

Msh2 separation of function mutations confer defects in the initiation steps of mismatch repair.

In eukaryotes the MSH2-MSH3 and MSH2-MSH6 heterodimers initiate mismatch repair (MMR) by recognizing and binding to DNA mismatches. The MLH1-PMS1 heterodimer then interacts with the MSH proteins at or near the mismatch site and is thought to act as a mediator to recruit downstream repair proteins. Here we analyzed five msh2 mutants that are functional in removing 3' non-homologous tails during double-strand break repair but are completely defective in MMR. Because non-homologous tail removal does not require MSH6, MLH1, or PMS1 functions, a characterization of the msh2 separation of function alleles should provide insights into early steps in MMR. Using the Taq MutS crystal structure as a model, three of the msh2 mutations, msh2-S561P, msh2-K564E, msh2-G566D, were found to map to a domain in MutS involved in stabilizing mismatch binding. Gel mobility shift and DNase I footprinting assays showed that two of these mutations conferred strong defects on MSH2-MSH6 mismatch binding. The other two mutations, msh2-S656P and msh2-R730W, mapped to the ATPase domain. DNase I footprinting, ATP hydrolysis, ATP binding, and MLH1-PMS1 interaction assays indicated that the msh2-S656P mutation caused defects in ATP-dependent dissociation of MSH2-MSH6 from mismatch DNA and in interactions between MSH2-MSH6 and MLH1-PMS1. In contrast, the msh2-R730W mutation disrupted MSH2-MSH6 ATPase activity but did not strongly affect ATP binding or interactions with MLH1-PMS1. These results support a model in which MMR can be dissected into discrete steps: stable mismatch binding and sensing, MLH1-PMS1 recruitment, and recycling of MMR components.

Adenosine Triphosphatases↗
PubMed2001

Genotype and phenotype in hereditary nonpolyposis colon cancer: a study of families with different vs. shared predisposing mutations.

Hereditary nonpolyposis colorectal cancer (HNPCC) is a multi-organ cancer syndrome associated with heritable mutations in DNA mismatch repair genes, particularly MLH1 (MutL Homologue 1) and MSH2 (MutS Homologue 2). We took advantage of the unique characteristics of the Finnish HNPCC families to assess genotype- phenotype correlations in this disorder. We studied 295 mutation carriers (10 mutations in MLH1 and 3 in MSH2) segregating in 55 families. In addition to the comparison of families with different mutations, the enrichment of two MLH1 mutations, one affecting exon 16 (29 families, 186 individuals) and another one affecting exon 6 (10 families, 45 individuals) allowed the comparison of kindreds with identical predisposing mutations. Extracolonic cancers were more common in MSH2 than MLH1 mutation carriers, with the ratios of 0.48 and 0.64, respectively, of colorectal cancer to all cancers (P = 0.076). Within MLH1, two mutations affecting only the amino terminal portion showed a significant association with late onset of cancer as compared to the remaining mutations. Importantly, families with the MLH1 exon 16 mutation displayed significant variation (P = 0.012) in the age at onset of colon cancer, despite shared predisposition. We conclude that even though characteristics of the inherited mutations may explain part of the observed clinical variation, other factors have a significant impact on HNPCC phenotype determination.

Adaptor Proteins, Signal Transducing↗
PubMed1998

Clinical findings with implications for genetic testing in families with clustering of colorectal cancer.

BACKGROUND: Germ-line mutations in DNA mismatch-repair genes (MSH2, MLH1, PMS1, PMS2, and MSH6) cause susceptibility to hereditary nonpolyposis colorectal cancer. We assessed the prevalence of MSH2 and MLH1 mutations in families suspected of having hereditary nonpolyposis colorectal cancer and evaluated whether clinical findings can predict the outcome of genetic testing. METHODS: We used denaturing gradient gel electrophoresis to identify MSH2 and MLH1 mutations in 184 kindreds with familial clustering of colorectal cancer or other cancers associated with hereditary nonpolyposis colorectal cancer. Information on the site of cancer, the age at diagnosis, and the number of affected family members was obtained from all families. RESULTS: Mutations of MSH2 or MLH1 were found in 47 of the 184 kindreds (26 percent). Clinical factors associated with these mutations were early age at diagnosis of colorectal cancer, the occurrence in the kindred of endometrial cancer or tumors of the small intestine, a higher number of family members with colorectal or endometrial cancer, the presence of multiple colorectal cancers or both colorectal and endometrial cancers in a single family member, and fulfillment of the Amsterdam criteria for the diagnosis of hereditary nonpolyposis colorectal cancer (at least three family members in two or more successive generations must have colorectal cancer, one of whom is a first-degree relative of the other two; cancer must be diagnosed before the age of 50 in at least one family member; and familial adenomatous polyposis must be ruled out). Multivariate analysis showed that a younger age at diagnosis of colorectal cancer, fulfillment of the Amsterdam criteria, and the presence of endometrial cancer in the kindred were independent predictors of germ-line mutations of MSH2 or MLH1. These results were used to devise a logistic model for estimating the likelihood of a mutation in MSH2 and MLH1. CONCLUSIONS: Assessment of clinical findings can improve the rate of detection of mutations of DNA mismatch-repair genes in families suspected of having hereditary nonpolyposis colorectal cancer.

Adaptor Proteins, Signal Transducing↗